My Chevrolet S10's battery light kept coming on while I was driving, and today it was driving just fine all day but when night came it died on me.
I saw my dash lights began to dim so when I came to a complete stop it just shut off and wouldn't crank unless I jumped it off. After a few minutes of letting it charge it cranked right up all my lights, radio etc. was on but as soon I take the jumper cables off the battery it dies.
Do I have a dead battery or is my alternator bad?
Unfortunately I suspect the answer is both - from what you've described I think the alternator has been failing for a while, and the increased discharge from the battery has probably caused that to fail as well. It may be that the battery can be revived with a good, long, deep charge, but even if it can I suspect it's lifetime will be much shortened.
The battery isn't holding sufficient charge to power the vehicle's electrics. This could be due to:
a failing alternator
So something about the alternator or regulator is not allowing it to put out the requisite voltage and current.
high voltage drop across the battery-charging circuit
Here the alternator is actually doing its job, but things like corrosion around the battery's terminals are robbing it of electron juice.
a kaput battery
The charging system works fine, but the battery can't retain charge (dead cells, etc.)
